The present disclosure relates to a cathode active material, its manufacturing method, a cathode, its manufacturing method, and a secondary battery and, more particularly, to a cathode active material containing a lithium composite oxide.
In recent years, in association with the realization of advanced performance and multi-function of mobile equipment, the realization of a large capacitance of a secondary battery as a power source of such mobile equipment is earnestly requested. As a secondary battery which can satisfy such a request, a large attention has been paid to a non-aqueous electrolyte secondary battery in which lithium cobalt acid is used as a cathode, graphite is used as an anode, and an organic mixed solvent containing a lithium salt supporting electrolyte is used as an electrolyte.
In the non-aqueous electrolyte secondary battery in the related art which operates at the maximum voltage of 4.2V, the cathode active material such as lithium cobalt acid which is used as a cathode uses a capacitance of up to about 60% of its theoretical capacitance. Therefore, a residual capacitance can be used in principle by further raising the charge voltage. Actually, it has been known that a high energy density can be realized by raising an upper limit voltage upon charging to 4.25V or more (for example, refer to Patent Document 1: pamphlet of International Publication No. 03/019713). To satisfy a request for the realization of a larger capacitance, in recent years, an anode of a large capacitance using silicon Si, germanium Ge, tin Sn, or the like has also vigorously been examined.
The foregoing non-aqueous electrolyte secondary battery is mainly used in mobile equipment such as notebook-sized personal computers, cellular phones, or the like and is often subjected to a relatively high temperature environment for a long time due to heat which is generated from the equipment, heat in a moving vehicle, or the like. If the non-aqueous electrolyte secondary battery in a charging state is left in such an environment, a gas is generated by a reaction of the cathode and an electrolytic solution. Particularly, in the non-aqueous electrolyte secondary battery whose upper limit voltage upon charging has been set to 4.25V or more, the reaction of the cathode and the electrolytic solution increases and an amount of generated gas increases.
For example, in the case where the non-aqueous electrolyte secondary battery has been enclosed in a sheathing member made of a laminate film, if the gas is generated as mentioned above, sometimes, such a problem that the sheathing member is expanded, its thickness increases, and its size is out of the standard of a battery enclosing portion of electronic equipment occurs. Such a problem that an internal resistance of the battery increases by the reaction of the cathode and an electrolytic solution and it is difficult to take out a sufficient capacitance also occurs.
It is, therefore, desirable to provide a cathode active material, its manufacturing method, a cathode, its manufacturing method, and a secondary battery in which excellent high-temperature preserving characteristics can be obtained.